1. Field of the Invention
The present invention is related to the field of land surveying and more particularly to a stadia rod having an automatic elevation read-out display capability and a method for using the stadia rod.
2. Description of the Related Art
Stadia rods are used by surveyors in conjunction with an optical level or a laser level to determine the differences in vertical elevation from a point of known elevation and to that of another point or points.
The method used for centuries has been to view a stadia rod through an optical level. Markings provided on the stadia rod show exact graduations in a given scale, such as meters or feet, starting at the bottom and increasing incrementally up the rod. For example, if the rod is 8 feet in length, the top of the rod is marked 8′0″. Most commonly, surveyor's rods in the U.S. are marked in feet, as well as in tenths and hundredths of a foot. The height on the rod does not typically represent the actual elevation, but is used in the calculation thereof.
In the 20th century, a rod was developed called a Lenker Rod, in which the surface bearing the lineal dimensional graduations is an endless tape, ten feet in length. The tape, which is mounted on a rectangular rod with a recessed track on the front and back to hold the tape, can be moved around the rod by sliding and then mechanically held in a fixed position as desired by the user. The markings are opposite that of a standard stadia rod, i.e., they increase going down the rod. Therefore, when an object having an elevation higher than the established base elevation is recorded, the reading is higher. Conversely, if the object whose elevation is desired is lower than that of the base or known elevation, the reading is lower. All readings are direct but are limited to less than 5′0″ because only half of the tape is viewable without starting over in the loop.
In U.S. Pat. No. 4,030,832 to Rando et al., a grade rod with a laser beam generator is used to determine elevations and grades, along with a beam detector with photocells and traveling tape assembly movable with a slider. With the laser beam generator operating at a location remote from the grade rod, the slider moves up and/or down in a search mode until the laser beam activates one of the photocells thereon. The system then enters an automatic tracking mode until the slider is determined to be centered on the beam, at which point the tape assembly on the rod may be read to determine elevation. This grade rod mechanism is highly complex and cumbersome to use.
According to U.S. Pat. No. 3,469,919 to Zellner, an electronic surveying instrument having a sending station is placed at a benchmark location of known elevation where the laser is leveled. A receiver station is placed at a surface location where it is desired to measure the elevation. The stand of the receiver station includes a surveying rod having a stationary member slidingly connected to a reciprocal or sliding member by an adjustable bracket, the sliding member having two antennae. While the sending station transmits a horizontal beam at the benchmark elevation, the sliding member is reciprocated until both of the antennae are activated indicating that the received beam is located at the juxtaposition of the antennae. Indicia on the members, may then be read to determine the height of the beam plane with respect to the surface location, from which elevation may be calculated. This system is also quite complex and does not provide a direct read-out of the elevation. The Zellner patent also requires laser transmission from a benchmark location of known elevation which limits the flexibility of the system.
U.S. Pat. No. 4,673,287 to Rickus includes a laser-optical surveying system that provides a leveling system in which a laser transmitter transmits a horizontal beam to a surveyor's rod which is equipped with a photoelectrically sensitive layer having coding therein for identifying the location, i.e., altitude, on the rod that is activated by the passing laser beam. This altitude information may then be displayed, stored or processed, but is limited to identifying only a given height on the rod, and does not provide a direct read-out of actual elevation.
All of these systems have limitations in terms of automatic elevation display, most of these devices being highly complex and commensurately expensive. Accordingly, a need exists for a system having automatic elevation sensing and display capability in a device that can be conveniently carried and which is simple and inexpensive to use.